rawsocket和recvfrom php socket recvfrom

A protocol of IPPROTO_RAW implies enabled IP_HDRINCL and is able to send       any IP protocol that is specified in the passed header.  Receiving of all       IP protocols via IPPROTO_RAW is not possible using raw sockets.

在用raw socket写一个Ping程序；
最开始的时候多方参考，不巧参考的程序特性各异并且功能较为复杂，所以我一开始写的程序就复杂化了；创建raw sock的时候直接使用了IPPROTO_RAW；
知道通过设置IP_HDRINCL可以控制IP header，但是不知道上面那句话；
本来以为IPPROTO_RAW是一个通用协议呢..

不管怎么样，在开始只发送包的时候，程序当中自己设置了ip header，所以没啥问题；
但是当希望recvfrom的时候问题出来了：在发送ping的sockfd接口收不到任何包；具体问题是recvfrom不会返回；
郁闷了一会儿；
灵光一闪，把raw改成IPPROTO_ICMP，recvfrom返回是返回了，但是wireshark现实icmp的类型是69，不认识~~
认真分析包发现 69是0x45，同时包的长度增加了20；那就很容易理解了，多了一个IP包头；
也即IPPROTO_ICMP不需要自己设置IP头部么~~

因为代码中太多的IP头设置，因此仍然保留了RAW；为了接收包，新定义一个recvfd，类型是IPPROTO_ICMP；
需要注意的是
recvfd应该在发包之前定义，这样，发送的ping包的回复可以及时地送到这个端口；

哎呀，果然是写写程序才真的明白阿~~
贴一下代码，会比较有成就感 哈哈

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include
#include 
#include 

char buff[28]={0};
int sockfd;
struct sockaddr_in target;

unsigned short in_cksum(unsigned short *addr, int len)
{
 int sum=0;
 unsigned short res=0;
 while( len > 1) {
 sum += *addr++;
 len -=2;
 // printf("sum is %x.n",sum);
 }
 if( len == 1) {
 *((unsigned char *)(&res))=*((unsigned char *)addr);
 sum += res;
 }
 sum = (sum >>16) + (sum & 0xffff);
 sum += (sum >>16) ;
 res = ~sum;
 return res;
}



int main(int argc, char * argv[]){

 int send, recv,i;
 send = 0;
 recv = 0;
 i = 0;

 if(inet_aton(argv[1],&target.sin_addr)==0){
  printf("bad ip address %sn",argv[1]);
  exit(1);
 }

 int recvfd = socket(AF_INET,SOCK_RAW,IPPROTO_ICMP);
 struct ip *ip = (struct ip *)buff;
 struct icmp * icmp = (struct icmp*)(ip+1);

 if((sockfd=socket(AF_INET,SOCK_RAW,IPPROTO_RAW))<0)
 { perror("socket error!");exit(1); }

 ip->ip_v = 4;
 ip->ip_hl = 5;
 ip->ip_tos = 0;
 ip->ip_len = htons(28);
 ip->ip_id = htons(8);
 ip->ip_off = htons(0);
 ip->ip_ttl = 65;
 ip->ip_p = IPPROTO_ICMP;
 ip->ip_sum = 0;
 ip->ip_src.s_addr = target.sin_addr.s_addr;
 ip->ip_dst.s_addr = target.sin_addr.s_addr;

 icmp->icmp_type = ICMP_ECHO;
 icmp->icmp_code = 0;
 icmp->icmp_cksum = 0;
 icmp->icmp_id = 2;
 icmp->icmp_seq = 3;

 while(send < 4)
 {
 send++;
// icmp->icmp_seq = icmp->icmp_seq+1;
 icmp->icmp_cksum = 0;
 icmp->icmp_cksum = in_cksum((unsigned short *)icmp,8);
 sendto(sockfd, buff, 28,0,(struct sockaddr *)&target,sizeof(target));
 sleep(1);
 }

 struct sockaddr_in from;
 int lenfrom = sizeof(from);

 char recvbuff[1024];
 int n;
 //printf("recvfd is %dn",recvfd);  
 while(recv<4){
  if((n = recvfrom(recvfd,recvbuff,sizeof(recvbuff),0,(struct sockaddr *)&from,&lenfrom))<0) {perror("receive error!n");exit(1);}; 
  struct ip *ip=(struct ip *)recvbuff;
  struct icmp *icmp = (struct icmp*)(ip+1);
//  printf("n is %d,ip header length is %dn ",n,ip->ip_hl);
  if((n-ip->ip_hl*4)<8) {printf("Not ICMP Reply!n");break;}
  if((icmp->icmp_type==ICMP_ECHOREPLY)&&(icmp->icmp_id==2)){
   printf("%d reply coming back from %s: icmp sequence=%u ttl=%dn",recv+1,inet_ntoa(from.sin_addr),icmp->icmp_seq,ip->ip_ttl);

  recv++;}


 } 

 return 0;
}

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